Monitor base



FIG. 1 is a perspective view of a monitor base, showing my new design;

FIG. 2 is a front view thereof;

FIG. 3 is a rear view therefore;

FIG. 4 is a left side view thereof;

FIG. 5 is a right side view thereof;

FIG. 6 is a top view thereof; and,

FIG. 7 is a perspective view of a monitor base in use.

The portions of the monitor base shown in broken lines form no part of the claimed design. 

The ornamental design for a monitor base, as shown and described. 